Laser alignment systems have been used for years, and some of these systems use a rotating laser light source that periodically sweeps 360°, thereby creating a plane of laser light that can be received and detected by a laser light receiver. Other types of laser alignment systems use a transmitter that projects laser energy continuously in a reference cone, or a reference plane, of light that spreads in all directions about a 360° circle. The range of such detection units, especially when used in direct sunlight, is greatly increased by modulating the laser light source at a predetermined frequency. Such a laser light alignment system using a modulated laser light source is disclosed in U.S. Pat. No. 4,756,617.
It is desirable to increase the effective range of such modulated laser light receivers. One way to do so is to increase the signal-to-noise ratio of the detection circuit.